In recent years, as semiconductor devices have had higher integration and higher density, wiring of circuits has become further finer and the number of layers of multilayer wiring has increased. In order to realize multilayer wiring while realizing finer circuits, it is necessary to perform planarization processing on surfaces of semiconductor devices with high accuracy.
As a technique for planarizing surfaces of semiconductor devices, CMP (Chemical Mechanical Polishing) is known. A polishing device for performing CMP is provided with a polishing table to which a polishing pad is attached and a top ring for holding an object to be polished (a substrate such as a semiconductor wafer or any of various films formed on a surface of a substrate) (hereinafter, referred to as “polishing target object”). The polishing device polishes the polishing target object by pressing on the polishing pad the polishing target object held by the top ring while rotating the polishing table.
The polishing device is being widely used in a polishing process in which an electrically conductive film such as a barrier film or a metal film formed on a surface of a substrate is polished. Detection of an end point of the polishing process and determination of a change in polishing conditions during polishing are performed on the basis of the thickness of the conductive film. Therefore, the polishing device is ordinarily provided with a film thickness detector for detecting the thickness of the conductive film during polishing. A typical example of the film thickness detector is an eddy current sensor.
The eddy current sensor is disposed in the polishing table and rotates with the rotation of the polishing table. The eddy current sensor has a coil connected to an alternating current power supply. The eddy current sensor generates a magnetic field by the coil while passing below the polishing target object with the rotation of the polishing table. An eddy current is thereby induced in the conductive film of the polishing target object. The magnitude of the eddy current changes according to the resistance of the conductive film, i.e., the film thickness of the conductive film. The eddy current sensor is arranged to detect the thickness of the conductive film from a change in the magnetic field generated by the eddy current induced in the conductive film.
While the polishing target object is being polished, heat is generated by friction between the polishing target object and the polishing pad. The output from the eddy current sensor possibly drifts due to an increase in ambient temperature around the eddy current sensor caused by the heat.
It is known that, in a first conventional technique as disclosed in National Publication of International Patent Application No. 2009-500829, a temperature sensor is provided around the eddy current sensor and temperature drift of the eddy current sensor is corrected according to the temperature detected by the temperature sensor.
It is also known that, in a second conventional technique as disclosed in Japanese Patent Laid-Open No. 2013-36881 and Japanese Patent Laid-Open No. 2005-121616, an amount of correction with respect to temperature drift is obtained by using an output signal from the eddy current sensor issued when the polishing target object is not present above the eddy current sensor.
The eddy current sensor is disposed in a hole formed in the polishing table and is opposed to the polishing target object, with the polishing pad interposed therebetween. The eddy current sensor has a sensor coil including an excitation coil and a detection coil. The excitation coil is connected to an alternating current power supply and produces a magnetic field, thereby inducing an eddy current in the polishing target object, e.g., a conductive film. The magnitude of the eddy current changes according to the resistance of the polishing target object, i.e., the film thickness of the polishing target object. With the detection coil, the thickness of the polishing target object is detected from a change in a magnetic field generated by the eddy current induced in the polishing target object. The eddy current sensor is used not only to measure the thickness of the polishing target object but also to measure the distance from the eddy current sensor to a measurement target object. That is, since the magnitude of the eddy current induced in the measurement target object changes according to the distance between the eddy current sensor and the measurement target object, the distance to the measurement target object is detected with the detection coil from a change in the magnetic field generated by the eddy current induced in the measurement target object.